U.S. patent application number 17/437648 was filed with the patent office on 2022-05-26 for improved coating processes.
This patent application is currently assigned to Nanofilm Technologies International Limited. The applicant listed for this patent is Nanofilm Technologies International Limited. Invention is credited to Zhang Yang RONG, Xu SHI, Zhi TANG.
Application Number | 20220162739 17/437648 |
Document ID | / |
Family ID | 1000006192722 |
Filed Date | 2022-05-26 |
United States Patent
Application |
20220162739 |
Kind Code |
A1 |
SHI; Xu ; et al. |
May 26, 2022 |
IMPROVED COATING PROCESSES
Abstract
A method of depositing a coating on a substrate comprises
simultaneously depositing a first material via a CVA process and a
second material via a sputtering process; also described are
coatings obtained therefrom and coated substrates.
Inventors: |
SHI; Xu; (Singapore, SG)
; TANG; Zhi; (Singapore, SG) ; RONG; Zhang
Yang; (Singapore, SG) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nanofilm Technologies International Limited |
Singapore |
|
SG |
|
|
Assignee: |
Nanofilm Technologies International
Limited
Singapore
SG
|
Family ID: |
1000006192722 |
Appl. No.: |
17/437648 |
Filed: |
March 13, 2020 |
PCT Filed: |
March 13, 2020 |
PCT NO: |
PCT/EP2020/056864 |
371 Date: |
September 9, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 14/165 20130101;
C23C 14/0605 20130101; C23C 14/025 20130101; C23C 14/325 20130101;
C23C 14/35 20130101 |
International
Class: |
C23C 14/06 20060101
C23C014/06; C23C 14/32 20060101 C23C014/32; C23C 14/35 20060101
C23C014/35; C23C 14/16 20060101 C23C014/16; C23C 14/02 20060101
C23C014/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 15, 2019 |
EP |
19163306.4 |
Claims
1. A method of depositing a coating on a substrate, the method
comprising simultaneously depositing a first material via a CVA
process and a second material via a sputtering process,
characterised in that the first material comprises to-C.
2. A method according to claim 1 of depositing a coating comprising
a first material and a second material on a substrate, the method
comprising: i) depositing the first material via a CVA process to
form a lower layer; ii) simultaneously depositing the first
material via the CVA process and the second material via a
sputtering process to form a transition layer; and iii) depositing
the second material via a sputtering process to form an upper
layer.
3. A method according to claim 1 of depositing a coating comprising
a first material and a second material on a substrate, the method
comprising: i) depositing the second material via a sputtering
process to form a lower layer; ii) simultaneously depositing the
first material via the CVA process and the second material via a
sputtering process to form a transition layer; and iii) depositing
the first material via a CVA process to form an upper layer.
4. A method according to claim 1, wherein the CVA process is
FCVA.
5. A method according to claim 1, wherein the first material
consists of to-C.
6. A method according to claim 1, wherein the second material is
selected from Ti, Cr, Si, Zr, C, W and alloys and compounds
thereof.
7. A method according to claim 1, further comprising depositing a
seed layer onto the substrate prior to coating it with the first
and second materials, and optionally wherein the seed layer has a
thickness of from 0.1 .mu.m to 0.5 .mu.m.
8. A method according to claim 1, wherein the substrate is a
metallic substrate.
9. A method according to claim 8 wherein the substrate is a steel
substrate.
10. A method according to claim 2 wherein the first layer has a
thickness of 0.2 .mu.m to 1.5 .mu.m, and/or the second layer has a
thickness of 0.1 .mu.m to 0.3 .mu.m.
11. A method according to claim 1 wherein the coating has a
thickness of from 0.5 .mu.m to 5 .mu.m.
12. A method according to claim 11 wherein the coating has a
thickness of from 1.0 .mu.m to 3.0 .mu.m.
13. A method according to claim 1 wherein the coating takes place
in a chamber at a pressure of 0.5 Pa or less.
14. A coated substrate obtainable from a method according to claim
1.
15. A substrate coated with a coating, wherein the coating
comprises: i) a layer deposited via a sputtering process; ii) a
transition layer between (i) and (iii) deposited by a process
comprising simultaneous CVA deposition and a sputtering process;
and iii) a ta-C layer deposited by CVA deposition.
16. A coating apparatus comprising: a substrate station, for
location of a substrate to be coated; a CVA station, for depositing
ta-C via CVA onto the substrate; a sputtering station, for
depositing material via a sputtering process onto the substrate;
and a control unit that is capable of operating the CVA and
sputtering stations simultaneously.
Description
INTRODUCTION
[0001] This present invention relates to coatings with improved
properties produced by a combination of sputtering and other
processes and methods for producing such coatings.
BACKGROUND TO THE INVENTION
[0002] A large variety of deposition techniques are used to coat
substrates. Vapor deposition technology is typically used to form
thin film deposition layers in various types of applications,
including microelectronic applications and heavy-duty applications.
Such deposition technology can be classified in two main
categories. A first category of such deposition technology is known
as Chemical Vapor Deposition (CVD). CVD generally refers to
deposition processes occurring due to a chemical reaction. Common
examples of CVD processes include semiconducting Si layer
deposition, epitaxy and thermal oxidation.
[0003] A second category of deposition is commonly known as
Physical Vapor Deposition (PVD). PVD generally refers to the
deposition of solid substances occurring as a result of a physical
process. The main concept underlying the PVD processes is that the
deposited material is physically transferred onto the substrate
surface via direct mass transfer. Typically, no chemical reaction
takes place during the process and the thickness of the deposited
layer is independent of chemical reaction kinetics as opposed to
CVD processes.
[0004] Sputtering is a known physical vapor deposition technique
for depositing compounds on a substrate, wherein atoms, ions or
molecules are ejected from a target material (also called the
sputter target) by particle bombardment so that the ejected atoms
or molecules accumulate on a substrate surface as a thin film.
[0005] Another known physical vapor deposition technique is
cathodic vapor arc (CVA) deposition methods. In this method, an
electric arc is used to vaporize material from a cathode target.
Consequently, the resulting vaporized material condenses on a
substrate to form a thin film of coating. Filtered cathodic vacuum
arc (FCVA) processes in particular produce clean, dense
coatings.
[0006] Amorphous carbon is a free, reactive form of carbon which
does not have a crystalline form. Various forms of amorphous carbon
films exist and these are usually categorised by the hydrogen
content of the film and the sp.sup.2:sp.sup.3 ratio of the carbon
atoms in the film.
[0007] In an example of the literature in this field, amorphous
carbon films are categorised into 7 categories (see table below
taken from "Name Index of Carbon Coatings" from Fraunhofer Institut
Schich- and Oberflachentechnik):
TABLE-US-00001 Amorphous Carbon Films Hydrogen-Free Hydrogenated
Modified Modified with Unmodified With metals Unmodified Metals
Non-metals sp.sup.2 sp.sup.3 sp.sup.2 sp.sup.2 or sp.sup.3 sp.sup.3
sp.sup.2 sp.sup.2 Hydrogen- Tetrahedral, Metal- Hydrogenated
Tetrahedral, Metal- Non-metal free hydrogen- containing, amorphous
hydrogenated containing, containing amorphous free hydrogen- carbon
amorphous hydrogenated hydrogenated carbon amorphous free carbon
amorphous amorphous carbon amorphous carbon carbon carbon a-C ta-C
a-C:Me a-C:H ta-C:H a-C:H:Me a-C:H:X
[0008] Tetrahedral hydrogen-free amorphous carbon (ta-C) is
characterised in that it contains little or no hydrogen (less than
5% mol, typically less than 2% mol) and a high content of sp.sup.3
hybridised carbon atoms (typically greater than 80% of the carbon
atoms being in the sp.sup.3 state).
[0009] Whilst the term "diamond-like carbon" (DLC) is sometimes
used to refer to all forms of amorphous carbon materials, the term
as used herein refers to amorphous carbon materials other than
to-C. Common methods of DLC manufacture use hydrocarbons (such as
acetylene), hence introducing hydrogen into the films (in contrast
to ta-C films in which the raw material is typically hydrogen free
high purity graphite).
[0010] In other words, DLC typically has an sp.sup.2 carbon content
of greater than 50% and/or a hydrogen content of 20% mol and above.
The DLC may be undoped or doped with metals or non-metals (see
table above).
[0011] A wide range of materials can be deposited by sputtering and
hence sputtering provides a method of producing a large variety of
coatings. However, coatings produced by sputtering tend to be less
hard and less wear resistant than coatings produced by other
methods, such as FCVA. This unfortunately limits their
application.
[0012] Whilst ta-C coatings produced via FCVA are significantly
harder than sputtered coatings, the final appearance of the
coatings are a monotonous grey colour and therefore the coatings
are not desirable for certain applications where the coating
aesthetics are also important.
[0013] US 2002/007796 A1 (Gorokhovsky), WO 02/070776 A1 (Commw
Scient and Ind Res 0), EP 0306612 A1 (Balzers Gochvakuum), EP
0668369 A1 (Hauzer Holding) and CN 108823544 A (Yang Jieping) all
describe coating apparatus comprising an arc source and a sputter
target. However, these documents do not describe coating a
substrate with ta-C. US 2017/121810 A1 (Avelar Araujo Juliano et
al) describes substrates coated with a metal and a diamond-like
layer. However, this document does not describe coating a substrate
with ta-C using an FCVA apparatus.
[0014] There therefore exists the need for sputter-based coatings
with a wider range of applications, but which also have greater
hardness and wear resistance compared to conventional sputtered
coatings, as well as a need for methods and apparatus to deposit
such coatings.
THE INVENTION
[0015] The inventor of the present application has developed a
coating method which provides a modification of sputtering-based
processes. In one use, the invention can produce a coating with a
layer deposited by sputtering, but with increased density and/or
hardness compared to conventional sputtered coatings.
[0016] It has been hitherto found that applying a sputtered
material directly onto a layer deposited via FCVA (or vice versa)
can result in poor adhesion between the two layers and therefore
make the resulting coating susceptible to fracture or breakage. A
co-deposition coating method described herein to form an
intermediate "adhesion-promoting" layer overcomes this problem.
Thus, in another use, the invention can provide a sputter coating
with improved adhesion to another coating, e.g. one deposited by a
FCVA method.
[0017] The present invention accordingly provides a method of
depositing a coating on a substrate, the method comprising
simultaneously depositing a first material via a CVA process and a
second material via a sputtering process.
[0018] As FCVA coating processes normally occur at pressures in the
milli-Pascal range, whereas sputtering usually requires inert gas
pressures of greater than 0.1 Pa, it was not previously envisaged
that the two coating processes (i.e. CVA and sputtering) could be
used simultaneously. However, the inventor of the present invention
has surprisingly found that the strong plasma flux generated during
CVA coating can reduce the pressure required for sputtering.
Accordingly, when performed alongside a CVA coating method, the
pressure at which sputtering can be carried out can be much lower
than previously expected. Examples discussed in more detail below
illustrate the co-deposition method being used.
[0019] The co-deposited layer producible according to the invention
can be used as an intermediate layer between a layer of a material
deposited via a CVA process and a layer of another material
deposited via a sputtering process. This intermediate layer
promotes adhesion of the two layers (compared to if the layer
deposited by CVA was applied directed to the layer deposited by
sputtering, or vice versa).
[0020] Accordingly, the invention also provides a method of
depositing a coating comprising a first material and a second
material on a substrate, the method comprising: [0021] i)
depositing the first material via a CVA process to form a lower
layer; [0022] ii) simultaneously depositing the first material via
the CVA process and the second material via a sputtering process to
form a transition layer; and [0023] iii) depositing the second
material via a sputtering process to form an upper layer.
[0024] Alternatively, the invention also provides a method of
depositing a coating comprising a first material and a second
material on a substrate, the method comprising: [0025] i)
depositing the second material via a sputtering process to form a
lower layer; [0026] ii) simultaneously depositing the first
material via a CVA process and the second material via a sputtering
process to form a transition layer; and [0027] iii) depositing the
first material via the CVA process to form an upper layer.
[0028] In this context a transition layer is located intermediate
between a CVA-deposited layer and a sputter-deposited layer,
whichever order in which they were deposited.
[0029] The invention also provides a substrate coated with a
multi-layer coating using a method as described herein.
[0030] The invention also provides a substrate coated with a
coating comprising: [0031] i) a layer deposited via a sputtering
process; [0032] ii) a transition layer between (i) and (iii)
deposited by a process comprising simultaneous CVA deposition and a
sputtering process; and [0033] iii) a layer deposited by CVA
deposition.
[0034] The invention further provides a coating apparatus
comprising: [0035] i) a substrate station, for location of a
substrate to be coated; [0036] ii) a CVA station, for depositing
material via CVA onto the substrate; [0037] iii) a sputtering
station, for depositing material via a sputtering process onto the
substrate; and [0038] iv) a control unit that is capable of
operating the CVA and sputtering stations simultaneously.
[0039] Thus, the invention enables coating of a substrate with a
material that can be deposited by sputtering, but with increased
hardness and wear resistance and without substantially compromising
the structural integrity of the coating.
DETAILED DESCRIPTION OF THE INVENTION
[0040] As discussed above, the term "tetrahedral amorphous carbon"
(ta-C) as used herein refers to amorphous carbon having a low
hydrogen content and a low sp.sup.2 carbon content.
[0041] Ta-C is a dense amorphous material described as composed of
disordered sp.sup.3, interlinked by strong bonds, similar to those
that exist in disordered diamond (see Neuville S, "New application
perspective for tetrahedral amorphous carbon coatings", QScience
Connect 2014:8, http://dx.doi.org/10.5339/connect.2014.8). Due to
its structural similarity with diamond, ta-C also is a very hard
material with hardness values often greater than 30 GPa.
[0042] For example, the ta-C may have a hydrogen content less than
10%, typically 5% or less, preferably 2% or less (for example 1% or
less). The percentage content of hydrogen provided here refers to
the molar percentage (rather than the percentage of hydrogen by
mass). The ta-C may have an sp.sup.2 carbon content less than 30%,
typically 20% or less, preferably 15% or less. Preferably, the ta-C
may have a hydrogen content of 2% or less and an sp.sup.2 carbon
content of 15% or less. The ta-C is preferably not doped with other
materials (either metals or non-metals).
[0043] By contrast, the term "diamond-like carbon" (DLC) as used
herein refers to amorphous carbon other than to-C. Accordingly, DLC
has a greater hydrogen content and a greater sp.sup.2 carbon
content than to-C. For example, the DLC may have a hydrogen content
of 20% or greater, typically 25% or greater, for example 30% or
greater. The percentage content of hydrogen provided here again
refers to the molar percentage (rather than the percentage of
hydrogen by mass). The DLC may have an sp.sup.2 carbon content of
50% or greater, typically 60% or greater. Typically, the DLC may
have a hydrogen content of greater than 20% and an sp.sup.2 carbon
content of greater than 50%. The DLC may be undoped or doped with
metals and/or non-metals.
[0044] The invention advantageously provides coatings formed from
sputtered materials with hardness and wear resistance.
[0045] The present invention provides a method ("Method A") of
depositing a coating on a substrate, the method comprising
simultaneously depositing a first material via a CVA process and a
second material via a sputtering process. FCVA is a preferred CVA
process.
[0046] Magnetron sputtering usually occurs under an Argon
atmosphere at a pressure of about 2 mTorr to 10 mTorr (0.27 Pa to
1.33 Pa). However, the normal working pressure for an FCVA coating
process is typically less than 2.0E-5 Torr (2.7mPa) and an
additional assisting gas (such as Ar) is not required. In a FCVA
process, the plasma is sustained by an arcing process.
[0047] The inventor of the present invention has found that despite
the different (and previously believed to be mutually exclusive)
conditions that are usually used for sputtering and CVA coating
processes, it is possible to coat substrates with these two
processes simultaneously.
[0048] The simultaneous co-deposition process may occur at
pressures between 0.3 mTorr and 1.5 mTorr (0.040 Pa and 0.20 Pa),
for example between 0.5 mTorr and 1.0 mTorr (0.067 Pa and 0.13Pa).
Whilst under such a low-pressure magnetron sputtering is not
usually effective by itself, using plasma generated by an FCVA
process, a glow discharge can start on a magnetron sputtering
cathode surface and sputtering can function normally.
[0049] Hence, in the presence of CVA plasma, sputtering processes
can operate at lower chamber pressures than previously believed
possible. In this way, FCVA deposition and sputtering deposition
can work together to deposit a layer formed from both the FCVA and
the sputtering materials. The co-deposited layer solves the
adhesion problem between layers formed by FCVA (e.g. to-C) and
sputtering layers by avoiding an abrupt transition between the
respective materials.
[0050] It is possible to make use of this simultaneous
co-deposition method in order to provide a multi-layer coating
comprising a layer deposited via a CVA method and another layer
deposited via a sputtering method, where the layer deposited using
the co-deposition methods promotes adhesion between the two
aforementioned layers. This transition layer is formed according to
Method A above.
[0051] Accordingly, the invention also provides a method ("Method
B") of depositing a coating comprising a first material and a
second material on a substrate, the method comprising: [0052] i)
depositing the first material via a CVA process to form a lower
layer; [0053] ii) simultaneously depositing the first material via
the CVA process and the second material via a sputtering process to
form a transition layer; and [0054] iii) depositing the second
material via a sputtering process to form an upper layer.
[0055] Alternatively, the lower layer may be deposited by
sputtering and the upper layer by CVA, with the transition layer
being formed by simultaneous CVA and sputtering processes. Again,
the transition layer (i.e. the layer deposited using a
co-deposition method) promotes adhesion between the lower and upper
layers. The transition layer is again formed according to Method A
above.
[0056] Therefore, the invention also provides a method ("Method C")
of depositing a coating comprising a first material and a second
material on a substrate, the method comprising: [0057] i)
depositing the second material via a sputtering process to form a
lower layer; [0058] ii) simultaneously depositing the first
material via a CVA process and the second material via a sputtering
process to form a second layer; and [0059] iii) depositing the
first material via the CVA process to form a third layer.
[0060] The terms "lower layer" and "upper layer" are terms relative
to the other layers described. There may be additional layers
beneath the lower layer and there may also be additional layers
above the upper layer. The lower layer is more proximal to the
substrate than the transition layer and upper layer and is hence
deposited before the transition and upper layers are deposited. The
upper layer is more distal from the substrate than the transition
layer and lower layer and is hence deposited after both the
transition and lower layers have been deposited.
[0061] The first material is preferably a carbon-containing
material, for example an amorphous carbon (such term including both
DLC and to-C). The first material preferably comprises or consists
of to-C. There may be several such first layers (e.g. all
comprising or consisting of to-C), with Young's modulus and/or
hardness remaining the same or increasing from layer to layer,
suitably peaking or culminating with the properties of an uppermost
ta-C layer, usually the one exposed on the outside of the coated
substrate.
[0062] The total thickness of the one or more layers deposited by
CVA only (i.e. the lower layer in Method B and the upper layer in
Method C) is typically from 0.05 .mu.m to 2 .mu.m, preferably from
0.1 .mu.m to 1.7 .mu.m, more preferably from 0.2 .mu.m to 1.5 .mu.m
and even more preferably from 0.5 .mu.m to 1.0 .mu.m.
[0063] An aim of the invention is to provide hard coatings which
are stable and able to maintain their hardness and wear resistance
at high temperatures. Coated substrates of the invention preferably
have a coating with a hardness of at least 800 HV, preferably 1000
HV or more. Coatings with a wide range of measured hardness values
within these ranges have been made (see examples below), including
coatings with hardness of approximately 1000 HV.
[0064] The second material may be the same as or different to the
first material, but is typically different to the first material.
The second material can be any material that can be deposited by
sputtering. The second material may be selected from Ti, Cr, Si,
Zr, Al, C, W and alloys and compounds thereof. The second material
may be selected depending on the desired property of the coating.
For example, when the second material is the uppermost layer of the
coating, the second material may be selected based on its colour to
impart a particular aesthetic property to the coating. Examples of
preferred second materials include CrSiC, CrWC, CrAlSICN and CrN;
note that this nomenclature indicates components of the material
but not their precise ratios.
[0065] The thickness of the layer deposited by sputtering (i.e. the
upper layer in Method B and the lower layer in Method C) is
typically from 0.05 .mu.m to 1.0 .mu.m, for example from 0.1 .mu.m
to 0.5 .mu.m, preferably from 0.2 .mu.m to 0.4 .mu.m.
[0066] Layers deposited via sputtering typically have lower
hardness and Young's modulus values compared to layers deposited
via a CVA process. This is particularly the case when the material
deposited via the CVA process is to-C. The second layer (i.e. the
layer deposited via simultaneous sputtering and CVA processes)
typically therefore has a Young's modulus and/or hardness value
which is intermediate between those of the first and third layers.
This has been found to promote adhesion.
[0067] As mentioned above, magnetron sputtering usually occurs at a
pressure of about 2 mTorr to 10 mTorr (0.27 Pa to 1.33 Pa), whereas
for CVA the normal working pressure is typically less than 2.0E-5
Torr (2.7 mPa). In the co-deposition step of the invention,
pressures of between 0.5 mTorr and 1.0 mTorr (0.067 Pa and 0.13 Pa)
have successfully been used to date.
[0068] Accordingly, for Methods B and C of the invention: [0069]
deposition of the first/second materials via an CVA process may
occur at pressures of 0.1 Pa or less, typically 10 mPa or less, for
example 3 mPa or less; and/or [0070] simultaneously deposition via
the CVA process and sputtering process may take place at a pressure
of from 0.05 Pa to 0.15 Pa, for example from 0.06 Pa to 0.13 Pa;
and/or [0071] deposition of the first/second materials via a
sputtering process may occur at pressures of 0.2 Pa or greater, for
example from 0.2 to 1.4 Pa.
[0072] Accordingly, in Method B, the pressure at which deposition
takes place increases from step i) to step ii) to step iii) and in
Method C, the pressure at which deposition takes place decreases
from step i) to step ii) to step iii).
[0073] The thickness of the transition layer is typically from 0.05
.mu.m to 1 .mu.m, for example from 0.05 .mu.m to 0.5 .mu.m,
preferably from 0.1 .mu.m to 0.3 .mu.m.
[0074] Choice of suitable substrate to be coated is not
particularly restricted in any way. Specific substrates include
plastics materials, ceramic materials, rubber, metals and graphite.
In one preferred method, the substrate is made from (comprises or
consists of) a metal (e.g. steel). In another preferred method, the
substrate is made from graphite.
[0075] The coating may further optionally comprise a seed layer
between the substrate and lower layer (i.e. the layer deposited via
CVA). The seed layer is included to promote adhesion of the lower
layer to the underlying substrate. The nature of the seed layer
will therefore depend on the nature of the substrate and the
material in the lower layer (i.e. the first material in Method B
and the second material in Method C). Examples of suitable seed
layers include materials comprising Cr, W, Ti, NiCr, Si or mixtures
thereof. When the substrate is a steel substrate, examples of
preferred materials for the seed layer are Cr and NiCr.
[0076] The thickness of the seed layer is typically from 0.05 .mu.m
to 1 .mu.m, for example from 0.05 .mu.m to 0.5 .mu.m, preferably
from 0.1 .mu.m to 0.5 .mu.m.
[0077] Accordingly, the total thickness of the coatings is
typically from 0.5 .mu.m to 5 .mu.m, preferably from 0.5 .mu.m to 3
.mu.m, most preferably from 1 .mu.m to 3 .mu.m.
[0078] The invention also provides a substrate coated with a
coating comprising: [0079] i) a layer deposited via a sputtering
process; [0080] ii) a transition layer between (i) and (iii)
deposited by a process comprising simultaneous CVA deposition and a
sputtering process; and [0081] iii) a layer deposited by CVA
deposition.
[0082] Optional and preferred embodiments for all aspects of the
coated substrate are as described elsewhere herein in relation to
methods of the invention. For example, the layer (iii) suitably
comprises or consists of to-C.
[0083] Specific types of coated substrates according to the
invention, comprise, in order: [0084] (a) a seed layer comprising
NiCr and having a thickness of from 0.1 .mu.m to 0.2 .mu.m; [0085]
(b) a first layer comprising to-C deposited by CVA and having a
thickness of from 0.4 .mu.m to 0.6 .mu.m; [0086] (c) a second layer
comprising to-C deposited by CVA and metal or metal alloy or metal
compound deposited by sputtering, the second layer having a
thickness of from 0.1 .mu.m to 0.2 .mu.m; and [0087] (d) a third
layer comprising the metal or metal alloy or metal compound
deposited by sputtering and having a thickness of 0.1 .mu.m to 0.2
.mu.m.
[0088] Other specific coated substrate types according to the
invention, comprise, in order: [0089] (a) a steel substrate; [0090]
(b) a seed layer comprising Cr deposited by sputtering and having a
thickness of from 0.1 .mu.m to 0.2 .mu.m; [0091] (c) a layer
comprising both to-C deposited by CVA and Cr deposited by
sputtering; [0092] (d) a layer comprising to-C deposited by CVA and
having a thickness of from 0.4 .mu.m to 0.6 .mu.m; [0093] (e) a
layer comprising both to-C deposited by CVA and metal or metal
alloy or metal compound deposited by sputtering and having a
thickness of from 0.1 .mu.m to 0.2 .mu.m; and [0094] (f) a layer
comprising the metal or metal alloy or metal compound deposited by
sputtering and having a thickness of 0.2 .mu.m to 0.4 .mu.m.
[0095] In the above, the coating comprises two co-deposited
transition layers of the invention. The first transition layer
(layer c) promotes adhesion between the seed layer and the ta-C
layer. The second transition layer (layer e) promotes adhesion
between the ta-C layer and the top, (coloured) sputtered layer.
[0096] Further specific coated substrates according to the
invention comprise, in order: [0097] (a) a graphite substrate;
[0098] (b) a sputtered seed layer of SiC and having a thickness of
from 0.1 .mu.m to 0.2 .mu.m; [0099] (c) a sputtered layer of
Si.sub.3N.sub.4 having a thickness of from 0.1 .mu.m to 1.0 .mu.m;
[0100] (d) a further sputtered layer of SiC having a thickness of
from 0.1 .mu.m to 0.2 .mu.m [0101] (e) a layer comprising both ta-C
deposited by CVA and SiC deposited by sputtering and having a
thickness of 0.1 .mu.m to 0.5 .mu.m; and [0102] (f) a layer
comprising ta-C deposited by CVA and having a thickness of from 0.4
.mu.m to 0.6 .mu.m.
[0103] The invention also provides a coating apparatus comprising:
[0104] a substrate station, for location of a substrate to be
coated; [0105] a CVA station, for depositing material via CVA onto
the substrate; [0106] a sputtering station, for depositing material
via a sputtering process onto the substrate; and [0107] a control
unit that is capable of operating the CVA and sputtering stations
simultaneously.
[0108] The substrate station, CVA station and sputtering station
are typically all located in a chamber of the apparatus. The
chamber is preferably also provided with a pump for controlling the
pressure within the chamber.
[0109] Typically, the CVA station is an FCVA station, for
depositing material via FCVA onto the substrate. The sputtering
station is suitably a magnetron sputtering station.
[0110] The optional and preferred features of the processes of the
present invention apply equally to the coating apparatus of the
present invention, in particular (but not limited to) the features
of the CVA and sputtering processes described herein.
[0111] Conventional sputtering and CVA processes are known and used
for a wide range of substrates and the methods of the invention are
similarly suitable for coating a wide range of substrates.
[0112] Coatings of the invention are multilayered and the
respective layers may be deposited using a range of known and
conventional deposition techniques, including CVD, PVD, HiPIMS,
magnetron sputtering and multi-arc ion plating. The CVA process is
typically a filtered cathodic vacuum arc (FCVA) process, e.g. as
described below. Apparatus and methods for FCVA coatings are known
and can be used as part of the methods of the invention. The FCVA
coating apparatus typically comprises a vacuum chamber, an anode, a
cathode assembly for generating plasma from a target and a power
supply for biasing the substrate to a given voltage. The nature of
the FCVA is conventional and not a part of the invention.
[0113] Hardness is suitably measured using the Vickers hardness
test (developed in 1921 by Robert L. Smith and George E. Sandland
at Vickers Ltd; see also ASTM E384-17 for standard test), which can
be used for all metals and has one of the widest scales among
hardness tests. The unit of hardness given by the test is known as
the Vickers Pyramid Number (HV) and can be converted into units of
pascals (GPa). The hardness number is determined by the load over
the surface area of the indentation used in the testing. As
examples. Martensite a hard form of steel has HV of around 1000 and
diamond can have a HV of around 10,000 HV (around 98 GPa). Hardness
of diamond can vary according to precise crystal structure and
orientation but hardness of from about 90 to in excess of 100 GPa
is common.
[0114] The invention advantageously provides coatings formed from
sputtered materials with increased hardness and wear
resistance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0115] The invention is now illustrated with reference to the
accompanying drawings in which:
[0116] FIG. 1 is a schematic diagram showing the structure of the
coating of the invention described in Example 1 (not to scale).
EXAMPLES
Example 1
[0117] A first example of the coating of the invention (see FIG. 1,
10) was prepared as described below:
TABLE-US-00002 Layer Thickness SPT* (14) 0.3 .mu.m ta-C + SPT* (13)
0.4 .mu.m ta-C (12) 0.8 .mu.m Substrate (11) - SUS304 Steel Total
Thickness ~1.5 .mu.m (determined by CAR2)
[0118] SPT*--a range of materials deposited by sputtering was used
to form a range of coatings with different coloured uppermost
layers:
TABLE-US-00003 SPT* material Colour CrSiC Charcoal CrWC Black
CrAlSiCN Blue CrN Silver
[0119] i. Start FCVA ta-C deposition first, gradually increasing
input Ar pressure to a pressure of between 0.5 to 1.0 mTorr ;
[0120] ii. Keep the pressure constant steady and begin magnetron
sputtering;
[0121] iii. After a certain time (e.g. a time period sufficient to
generate a co-deposited layer with a thickness of about 400 nm),
stop FCVA coating and continue sputtering to form the top layer
Example 2
[0122] The hardness of the coatings prepared in Example 1 were
determined by using a nanoindenter (CSM NHT2). These values were
compared with the hardness of coatings produced using sputtering
only (i.e. sputtering the SPT material directly onto the
substrate).
TABLE-US-00004 CrSiC CrWC CrAlSiCN CrN Hardness (HV) SPT only 680
500 660 1200 (Comparative Examples) SPT & ta-C 1250 950 1100
1530 (Example 1)
Example 3--Cross Hatch
[0123] To check the level of adhesion of the coating to the
substrate, a cross hatch test was conducted based on the ASTM
D-3359 Test Method B. A lattice pattern with grid dimensions of 1.0
mm by 1.0 mm was cut into the surface of the coating. Pressure
sensitive 51596 was then applied to the cut coating and
removed.
[0124] In both the coatings of Example 1 and the corresponding
Comparative Coatings (containing only a sputtered layer of the SPT
material), the peel-off area was less than 5%.
Example 4--Steel Wool Abrasion Test
[0125] As an indication of the wear-resistance of the coatings of
Example 1, a Taber abrasion test was conducted on the coatings,
with the following conditions: [0126] Instrument: Taber Linear
Abraser Test [0127] Abradant: Steel Wool [0128] Test Load: 500g
weight [0129] Cycle Speed: 60 cycles/min [0130] Stroke Length: 5
mm
[0131] After 400 cycles, there were no noticeable scratches on the
surface of the coatings of Example 1. When corresponding substrates
coated with only the SPT materials (i.e. without the ta-C layer or
the transition layer containing ta-C and SPT) were subject to the
same conditions, visible scratches were observed.
Example 5--Blue Jean Abrasion Test
[0132] As an indication of the wear-resistance of the coatings of
Example 1, a Taber abrasion test was conducted on the coatings,
with the following conditions: [0133] Instrument: Taber Linear
Abraser Test [0134] Abradant: Levis blue jean material [0135] Test
Load: 500 g weight [0136] Cycle Speed: 60 cycles/min [0137] Stroke
Length: 5 mm
[0138] After 1000 cycles, there were no noticeable scratches on the
surface of the coatings of Example 1. When corresponding substrates
coated with only the SPT material (i.e. without the ta-C layer or
the transition layer containing ta-C and SPT) were subject to the
same conditions, visible scratches were observed.
Example 6--Salt Spray Test
[0139] As an indication of the corrosion-resistance of the coatings
of Example 1, a salt spray test was conducted on the coatings. The
salt spray test was based on ASTM B117: Standard
[0140] Practice for Operating Salt Spray (Fog) and comprised
spraying a 5% salt water solution onto the coated substrates at a
temperature of 35.degree. C.
[0141] After 72 hours, there were no visible signs of rust or
degradation of the coatings of Example 1. When corresponding
substrates coated with only the SPT material (i.e. without the ta-C
layer or the transition layer containing ta-C and SPT) were subject
to the same conditions for 72 hours, corrosion was observed.
[0142] As can be seen in the Example above, coatings of the
invention can have increased hardness, wear resistance and
corrosion resistance compared to the comparative coatings.
* * * * *
References